Fabrication method for p-n junctions



May 7, 1957 v. ozARow FABRICATION METHOD FOR P-N JuNc'rIoNs Filed April s. 195:5

United States Patent O FABRICATION METHOD FOR P-N JUNCTIONS Vernon Ozarow, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application April 3, 1953, Serial No. 346,662

1 Claim. (Cl. 14S- 1.5)

This invention relates to a method of manufacturing semiconductor devices having predetermined uniform operating characteristics.

lt has been proposed that semiconductor devices can be made by heating a quantity of acceptor or donor meterial in contact with a body of semiconductor material. For example, an acceptor material such as indium and a semiconductor material such as N-type germanium may be used. During this process the indium spreads over an area of the germanium and penetrates into the germanium. This fusion or diffusion process of making semiconductor devices is more fully described and is claimed in copending Hall application, Serial No. 187,478, tiled September 29, 1950, and assigned to the assignee of this application. The depth of penetration depends on the duration and temperature of the heating process, the amount of indium and upon the size of the area attacked. Thus if the indium spreads out over a wide area, the depth of the penetration is less than if the indium spreads out over a small area.

For reasons well known to those skilled in the art, factors including the extent, shape and position of the area attacked by the indium and the depth of penetration may have a marked effect on the operating characteristics of a semiconductor device.

Therefore, it is an object of this invention to provide an improved method of manufacturing semiconductor devices in such manner as to control the factors noted above.

This objective may be attained by restricting and accurately positioning the area of the semiconductor material attacked by the electrically active material.

The manner in which these objectives may be attained may be more clearly understood after the following detailed consideration of the drawing which illustrates one of many possible ways in which the area of contact can be controlled in accordance with the principles of this invention. A body 2 of refractory material or other material that remains substantially inert at the temperature of the fusion of the electrically active material is placed against a block 4 of semiconductor material in such manner that any impurity material placed in the cavity 6 within the body 2 does not escape when it melts except by dissolving the portion of the block 4 at the bottom of the cavity. If the block 4 is in a horizontal position, it is not necessary to cover the top of the cavity 6, but if not, a piston 8, also made of refractory material,

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may be inserted into the cavity 6. The piston 8 can be made to exert a nearly constant pressure on the molten material in the cavity by the insertion of a compression spring 11 that is inserted between the outer end 10 of the piston 8 and the inside of a cover 12 that is secured to the body 2 of refractory material. It is apparent that the position of the area A may be accurately determined by moving the body of refractory material.

Some active materials like indium tend to draw up into a ball due to surface tension and, therefore, do not attack all of the surface A at the bottom of the cavity 6. However, application of pressure to the molten indium by the piston 8 overcomes the surface tension and causes the indium to attack substantially all of the surface A from the very beginning of the process. This insures more uniform penetration at all points of the surface. It is not necessary that the cover completely enclose the piston. Two such devices are shown but only one need be used if a diode is being manufactured.

The surface of contact A between the molten material and the block 4 of semiconductor material is determined by the cross sectional area of the cavity 6. The molten material penetrates the semiconductor body 4 and lies within a zone defined by a surface 14. The total volume between the surface 14 and the surface A depends on the temperature of the melt, the amount of molten material within the cavity 6 and the duration of the heat application.

While l have illustrated a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since various modifications both in the circuit arrangement and in the instrumentalities may be made, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

The method of making a semiconductor device comprising the steps of placing a mask of inert material against a body of semiconductor material so as to be in close contact with the surface thereof, the mask delining a restricted surface area, placing a material selected from the class of donor and acceptor materials within said area, applying heat so as to melt said material and cause it to penetrate the body of semiconductor material, applying pressure to said molten material within the mask so as to overcome the surface tension of the molten material and cause it to act on substantially all portions of the body of semiconductor material exposed within said mask, and removing said mask after the molten material has cooled.

References Cited in the tile of this patent UNITED STATES PATENTS 2,402,950 Culver July 2, 1946 2,518,253 Reis Aug. 8, 1950 2,561,579 Lenel July 24, 1951 2,597,028 Pfann May 20, 1952 2,612,443 Goetzel Sept. 30, 1952 2,629,672 Sparl Feb. 24, 1953 

